This invention relates to a binary data encoding system for converting a sequence of binary data to a sequence of binary codes suitable for the recording original binary data on a record medium such as a magnetic tape or a magnetic disc, and a decoding system for decoding and converting the sequence of converted binary codes upon reproducing it from the record medium.
In order to increase a recording density upon recording binary data on a record medium such as a magnetic tape or a magnetic disc there are previously proposed and practiced various encoding systems.
FIGS. 1(a)-(e) are explanatory diagrams of one example of a conventional encoding system. FIG. 1(a) shows one example of a bit pattern of an original binary data sequence wherein numerals 0 and 1 express logic "0" and "1" respectively and T.sub.o indicates a bit interval. FIGS. (b) and (d) are one example of conventional encoding systems; FIG. (b) is called an MFM system (modified FM system) and FIG. (d) is called a 3 PM system (3 position modulation system. As examples of sorts of appliances applied to the respective systems, the MFM system is used with magnetic disc devices (3330, 3340, 3350 etc.) of IBM and the 3 PM system is used with a magnetic disc device (8434) of Uniback. A conversion algorithm of the MFM system is to convert bits "1" and "0" of an original binary data sequence to "01" and "X0" respectively where "X" becomes a complementary logic (1.fwdarw.0 or 0.fwdarw.1) of a code bit just preceding thereto. Also, a conversion algorithm of the 3 PM system is to divide original data into 3-bit units to convert them to a 6-bit code as shown in the following 1st Table:
1ST TABLE ______________________________________ Conversion Algorithm of 3 PM System Original Converted Data Code Conditions ______________________________________ 000 000010 When a pattern of "101" 001 000100 is generated in a code 010 010000 sequence after the 011 010010 conversion it is 100 001000 changed to "010" 101 100000 110 100010 111 100100 ______________________________________
Furthermore a sequence of codes converted according to each of the encoding systems is such that recording currents are generated and recorded on a record medium so as to cause an inversion of magnetization with bits of "1" but not to cause an inversion of magnetization with bits of "0". FIGS. 1(c) and (e) are waveforms of the recording currents (NRZI signals) for the code sequences encoded according to the MFM system of FIG. (b) and the 3 PM systems of FIG. (d) respectively.
In the case where the recording is effected on a record medium,
(a) if a spacing between the inversions of magnetization (a recording wavelength) is shortened, then the magnetic transitions due to the leading and trailing inversions of magnetization interfere with each other so as to result in a cause for generating errors upon the decoding of a reproduced signal;
(b) even if a demodulation phase margin (Tw) (which will be described later) during the reproduction is small with respect to the spacing between the inversions of magnetization, the abovementioned errors are apt to be caused;
(c) if the spacing between the inversions of magnetization is long as compared with a period of a demodulating clock signal produced from a reproduced signal, then the demodulating clock signal can not be accurately produced from the reproduced signal and the abovementioned errors are apt to be caused; and
(d) if the spacing between the inversions of magnetization increases with respect to the ratio of its maximum to its minimum, then the reproduced signal increases in waveform interference (which is called a pattern peak shift) and the abovementioned errors are apt to be caused.
In general encoding systems, therefore, the undermentioned variables are given as the parameters indicating the ability system capability including the four items (a), (b), (c) and (d) as described above. Now assuming that in same encoding system, a sequence of m-bit binary data is converted to a sequence of n-bit binary codes (n.gtoreq.m) and, between a code bit "1" selected at will from the code sequence after the conversion and a code bit "1" next developed, there exist code bits "0" whose number has a minimum of d and a maximum of k, then the following expressions (1) to (4) hold: ##EQU1## where T.sub.0 is a period of the original data.
Accordingly, the foregoing description values of the expressions (1) and (2) are preferably larger (the abovementioned items (a) and (b)) and also the undermentioned ratio of the spacing between the inversions of maximum magnetization to the period of the demodulating clock signal (the expression (5)) and the undermentioned ratio of the spacing between the inversions of maximum magnetization to that between the inversions of minimum magnetization (the expression (6)) are preferably smaller (the abovementioned items (c) and (d)). ##EQU2##
With respect to the MFM system, the 3 PM system and the encoding system according to the present invention, the foregoing parameters are shown in the following 2nd Table:
2ND TABLE ______________________________________ Table of Comparison of Parameters in Respective Encoding Systems Parameter Spa. btwn. Spa. btwn. Spa. Invs. of Invs. of btwn. Max. Max. Magzn./ Invs. Magzn./ Spa. of Demodg. Period of btwn. Invs. Mod. Min. Phase Demodg. of Min. System Magzn. Marg. Clock Sig. Magzn. ______________________________________ MFM System 0.5 T.sub.0 0.5 T.sub.0 4 2 3 PM System 1.5 T.sub.0 0.5 T.sub.0 12 4 System of 1.5 T.sub.0 0.5 T.sub.0 9 3 This Invention ______________________________________